1. Field of the Invention
The subject matter disclosed generally relates to the field of semiconductor lasers.
2. Background Information
Semiconductor lasers are used in a variety of system applications. For example, semiconductor lasers are used as a light source in fiber optic communication systems. Laser diodes emit a laser beam from either the edge of the diode die or the surface of the die.
Individual diode laser sources have a finite output power. The output power of the laser source can be increased by providing an array of laser diodes. High powered laser diode arrays generate a relatively large amount of heat. For example, a 100 kW laser may generate one quarter of a megawatt of dissipated heat. The heat may affect the performance of the laser. For example, the
In order to dissipate this waste heat, high power laser diode arrays are traditionally soldered to coolers constructed of a high thermal conductivity material such as Copper which incorporate channels through which a cooling fluid such as water is circulated. Multiple layers of arrays mounted on coolers are stacked closely to generate high powers. This approach to cooling has several serious shortcomings:
In order to dissipate the high heat flux generated by the array, it is necessary to circulate large volumes of fluid through small cooling channels at high velocity. This results in a high rate of cooler failure due to erosion and clogging.
Secondly, these coolers have relatively high values of thermal impedance because a finite thickness of Copper separates the array from the cooling fluid. As a result, the temperature of the diode array is much higher than that of the cooling fluid, which causes degraded performance and lifetime.
Finally, the thermal expansion coefficient of the diode differs strongly from that of the cooler to which it is soldered. This places the diode array under considerable mechanical stress, which results in premature failure of the array.
Two-phase cooling technologies, such as spray or impingement cooling, utilize the latent heat-of-vaporization of fluids such as water or ammonia to greatly reduce the fluid flow and pressure required to dissipate a given quantity of waste heat. Two-phase cooling cannot be used to directly cool conventional diode arrays, because the spray interferes with the optical output of the laser array and damages the delicate diode output facet, resulting in failure. Two-phase techniques can indirectly cool a laser array by impingement on an intermediate heat exchanger, but this increases thermal impedance and negates the performance improvement.